There are many small, mid and big asteroids that have their elliptical orbits so close to Earth, that, while (in my opinion) are not so interesting to send (very risky) manned mission, are VERY interesting as "natural deep space probes" since they can fly in the Solar System without any "propellent" nor "engine", as explained in my latest article "Asteroids as Deep Space Probes":

An asteroid is not a free ride to anywhere in the solar system. The asteroid cannot change its orbit to go where you want, it just orbits in its own orbit like a moon or planet does. You can no more ride an asteroid to Jupiter than you can ride the Moon or Mars to Jupiter. If you are lucky enough to find an asteroid that is in an orbit that happens to come close to both Earth and Jupiter, the propellant needed by the space craft to rendezvous with that asteroid is exactly the same as would be needed to send the space craft to Jupiter on its own. The presence of absence of the asteroid has no effect on the amount of propellant needed.

You must understand that space craft are coasting without using any propulsion 99% of the time, just like an asteroid does. The only time the space craft uses propellant is to get set in the right orbit, then the engine is no longer needed. It isn't constantly using propellant as it flies. It technically isn't really flying, it is just orbiting, or moving on a ballistic path, which is to say a path controlled entirely by gravity and not by engine power.

the amount of propellent must be calculated on real missions, not as a generic claim

but, also assuming you're right, the asteroids as deep space probes give us many advantages

only a few probes is launched to the big targets (Jupiter, Mars, etc.) but the solar system is ways bigger and interesting

if many asteroids will be joined with a probe we can see the sun from a closer view, we can explore parts of the asteroids' belt where no probes will be never launched and to better know the space over the Pluto orbit where could be several objects we can't see with telescopes

last, we can use the asteroids that have the most useful orbits (near Mars, etc.) to carry VERY BIG PAYLOADS (a giant Mars Space Station, large resupply, land vehicles, etc.) to be released near Mars, etc.

I doubt, that send 500 mT (to be released near Mars) to an asteroid that run near Earth needs the SAME propellent than send it directly to Mars

also, the advantage could be even better if that materials (LOX, etc.) will be send to the asteroids from a moon base cutting the needed propellent to 1/6th

To get to it you have to match its course and velocity unless you want to try and impact it or grab on to it at some massive velocity.

If you have matched its orbit, then if you don't land on it you will still go out into deep space. Docking with the Asteroid takes almost no energy compared to matching its velocity, so it gives no propellant benefit.

However the benefits of creating a solar space station on an asteroid could be quite numerous. If you stabilised its attitude by exteneding a beam out from the surface then many possibilities arise.

The Asteroid's mass could protect equipment from debris and meteor showers. The Space station could function as relay to objects probes or planets on the far side of the sun, and it would form a stable deep space telescope platform.

If you are lucky enough to find an asteroid that is in an orbit that happens to come close to both Earth and Jupiter, the propellant needed by the space craft to rendezvous with that asteroid is exactly the same as would be needed to send the space craft to Jupiter on its own.

That's exactly what I thought. Furthermore, I thought it ages before you did, and I could prove it if my website hadn't been censored by Google, etc, etc

However the benefits of creating a solar space station on an asteroid could be quite numerous. If you stabilised its attitude by exteneding a beam out from the surface then many possibilities arise.

There could be benefits, but we need to know more about asteroids first. If by stabilising the attitude you mean despinning, you need to find a body with not too much spin in the first place. The current thinking is, I believe, that asteroids with significant spin are solid, whereas the slow-spinning ones are very likely 'rubble-piles' of loose material. The problem is applying any kind of force to it to cancel the spin, without simply disrupting the body and uprooting yourself.

idiom wrote:

The Asteroid's mass could protect equipment from debris and meteor showers. The Space station could function as relay to objects probes or planets on the far side of the sun, and it would form a stable deep space telescope platform.

We now know that many asteroids have small satellites, and there may be thousands too small to detect, ie a debris cloud. So it could be that while the asteroid will protect instruments from debris with high relative velocity, it is at the cost of placing it inside a cloud of debris with very low relative velocities. That and the asteroid itself would limit the view available to instruments, and you exchange an impact hazard for a contamination/abrasion hazard.

In general, tagging along with an asteroid will not help you characterize interplanetary space so much as cis-asteroidal space, which may be different.

So I think the balanced view is that these concepts are not to be dismissed out of hand, but we need to know more about asteroids. There has to be an assessment of any body of rock which you propose to exploit as a resource in any way, even just as the foundation for a building.

I think if we are going to support a space infrastructure with non-terrestrial resources, it makes sense to get materials from the smallest body that is easiest to get to - smaller bodies are easier to get away from. That is why NEOs are an important target for study, as well as further supporting the pure science objectives of the Dawn mission and others.

Meanwhile the budget for Arecibo - one of the very few radio telescopes capable of doing active radar observations on NEOs - is being cut again.

someday (this century or the next) when the Solar System will be colonized, the asteroids will be used as "interplanetary trains"

big payload in the range of thousands tons will be joined to small asteroids running a few millions km. from earth (using a low amount of propellent if sent from earth or lower if sent from moon factories) then, that payload will travel at zero costs the billion km. between earth and jupiter and, while it will be near it, will release the payload to fly and land on a colonized moon of jupiter (or saturn)

VERY BASIC knowledge of rockets say us that the payload falls while the distance increase... the same rocket can carry 10 mT to LEO or 5 mT to GEO or 2 mT to the Moon or a few hundreds kg. to Mars

That knowledge is a little TOO basic. In space travel the energy required to go somewhere is not related to the distance, it is related to the velocity change needed. Going to the Moon requires more propellant than going to low Earth orbit NOT because the Moon is farther away but because the rocket must leave Earth at 41,000 km/h to reach the Moon while it needs only 30,000 km/h to reach low Earth orbit.

gaetanomarano wrote:

if we send a payload to an asteroid that runs at 500,000 km. from earth, it needs an amount of propellent similar to a Moon travel, NOT for a Jupiter travel

Not true. It does not matter at all how close the asteroid comes to Earth. What matters is HOW FAST the asteroid is passing Earth. The Moon stays with Earth all the time but an asteroid in its own orbit around the Sun does not. A few asteroids are in orbits that come close to Earth and when they pass close to Earth, they do so at a high speed that must be equaled by the rocket trying to go to them. The rocket must arrive at the correct distance from Earth at the same moment as the asteroid and it must also SPEED UP to CATCH UP with that asteroid as is moves past that spot. The rocket needs to use up extra propellant to catch up with the asteroid. If it didn't, then either the asteroid would just pass the rocket at high speed, leaving it behind, or it would crash into the rocket and destroy it. An asteroid in an orbit that would pass Jupiter would be passing Earth much faster than one that only would go as far as Mars.

gaetanomarano wrote:

send large payloads to Jupiter, Saturn, etc. was possible thanks to the gravitational "slingshot" technique that allows to save the large amount of propellent of a direct launch.

That is because planets have a large Mass and strong gravity. The strong gravity is able to change the speed and direction of the rocket significantly during the short time it is close to the planet as it passes. But an asteroid has very weak gravity, and during the short time that it is close to the passing rocket its gravity will not be able to significantly alter the speed or direction of that rocket. The only way to get the benefit of that asteroid's speed as it passes would be to physically grab it, or get in front of it and let it crash into your rocket as it passes that spot at high speed. And the speed would be many thousands of kilometers per hour.